Roller cone drill bit



Nov. 26, 1968 R. REICHMUTH 3,412,817

. ROLLER CONE DRILL BIT Filed Nov. 10, 1965 INVEINTOR. Oomua 8 F/CHMUI'H 4 OPA/EX United States Patent Ofice Patented Nov. 26, 1968 3,412,817 ROLLER CONE DRILL BIT Donald R. Reichmuth, Austin, Tex., assignor to Continental Oil Company, Pouca City, Okla., a corporation of Delaware Filed Nov. 10, 1965, Ser. No. 507,172 9 Claims. (Cl. 175-341) ABSTRACT OF THE DISCLOSURE A roller cone rock bit having a cylindrical extension positioned at the apex of one or more of the roller cones, which cylindrical extension protrudes into the gap between the apices of the several roller cones and mills and fractures the small cone of material which tends to form in the center of a hole during drilling.

This invention relates to a roller cone type rock bit which can be utilized for drilling wells, such as those from which oil and gas are produced. More particularly, the present invention relates to a roller cone rock bit which is provided with drilling and earth fracturing structure at the lower or leading end of the bit to continually mill and fracture the drilled material which is disposed at the radial center and lowermost point in the well bore.

In the construction of roller cone type rock bits for drilling through relatively hard formations in the drilling of oil and gas wells, the roller cones are usually angled with respect to the vertical, and have their apices extended downwardly, and their axes of rotation converging in a common point on the vertical axis of rotation of the drill stem. Because of space limitations, many of the cones normally terminate in blunt points which necessarily leave a part of the bottom of the well bore along the axis thereof unfractured and uncut by the teeth of the bit. Rather, this central portion which is not milled or chipped away by the teeth of the bit is either eventually sheared off as a result of the extension of the hole downwardly in the formation on all sides of this central portion, or as the result of abrasion from circulating fluid and chips which are forced against this portion by the rotating bit.

In order to more effectively remove the portion of the formation at the center of the well bore, and below the lowest arts or apices of the several roller cones, it has previously been proposed to provide a structure termed a spear point on at least one of the cones, which structure can cut or gouge out the central portion of the hole as the bit moves downwardly in the earth.

It has also' been proposed in more recent roller cone constructions of the type in which a plurality of hard metal buttons are mounted on the cones, and used to accomplish the drilling by a compressive, crushing action, to mount a single protruding button on at least one of the cones, with the button protruding a part of the way into the space defined between the several apices of the cones at the center of the hole. This lead button is, like the other buttons, constructed of a relatively hard metal, such as tungsten carbide, and carries a rounded surface which permits it to bear against, and crush by compression, the burr or small cone which protrudes upwardly between the tips of the cones at the center of the Well bore. A construction of this type is shown in Morlan US. Patent 2,774,571.

It has recently been determined that it is desirable, in order to improve the efiiciency of the drilling operation, to cut away or fracture on a continuous basis, the burr or small cone which projects upwardly in the center of the well bore and which is usually beyond the reach of any of the regular cutter teeth on the cones. The basis for this discovery relative to the importance of maintaining a free surface for the teeth of the several roller cones to work against is set forth in US. patent application Ser. No. 232,558, entitled Drilling Method and Apparatus filed in the US. Patent Ofiice on Oct. 23, 1962, now abandoned, and assigned to the assignee of the present invention. The compression or crushing type action which is associated with the rounded or frusto-spherical button type insert, such as that shown in the Morlan patent, works fairly well where the peripheral surfaces of the roller cones lie in a substantially horizontal plane as there shown, but the efiiciency with which a flat, crushing type button of this character removes the small cone or burr which projects upwardly in the center of the bore hole is still dependent in large part upon the projection of the remaider of the hole downwardly around this central portion until the button can be brought to bear against the central portion of the formation in a way which enables a substantial portion of the weight of the drill string to be concentrated thereon.

The present invention provides an improvement in roller cone rock bits in which the advance with respect to prior types of rock bits resides primarily in the provision of a small, cylindrical extension positioned on the apex or point of at least one of the roller cones, and preferably on at least two thereof, which cylindrical extension protrudes into the gap or space existing betweenthe apices of the several roller cones, and functions to continually mill and fracture the small cone of material which tends to be formed in the center of the hole during the drilling operation. The cylindrical extension is constructed of an expecially hard metallic material, such as tungsten carbide, to permit it to withstand abrading and compressive forces applied thereto over a long operating period. In a preferred embodiment of the invention, the cylindrical extensions are small tungsten carbide, solid cylinders which are pressed into mating apertures or depressions formed in the tips or apices of the several roller cones, and which extend from the cones along the projected axes of rotation of the cones. The end face of each of the cylindrical extensions which lies outside of the depression or aperture into which the extension is pressed defines with the cylindrical side of the extension, a cutting edge which is oriented to be aligned with the cutting edges on the remainder of the teeth of the roller cones. These teeth are preferably disposed circumferentially around each of the roller cones so that the cutting edges thereof extend normal to radial lines projected from the central, vertically extending axis of rotation of the bit.

From the foregoing summary of the description, it will have become apparent that it is a major object of the present invention to provide a roller cone type rock bit having a hole centered milling element provided on at least one of the roller cones for the purpose of more efficiently advancing the bore hole into the ground along the central axis of the hole.

A further object of the invention is to provide an improved rock bit for use in drilling hard formations in which it is especially desired to maintain the perpendicularity of the hole during drilling.

Yet another object of the invention is to provide a roller cone type rock bit in which at least one of the roller cones of the bit carries a leading end portion which successfully resists wear and abrasion over long periods of time, thus imparting to the entire bit structure an effective service life of extended duration.

In addition to the foregoing described objects and advantages, additional objects and advantages will become apparent as the following detailed description of the invention is read in conjunction with the accompanying drawings which illustrate the invention.

In the drawings:

FIGURE 1 is a view in elevation of a three roller cone bit constructed in accordance with the present invention as the bit appears when one of the cones is, for clarity of depictions, rotated into the same plane as a second cone and is so shown in the drawing.

FIGURE 2 is an elevational view of the three cone bit as the cones would appear if viewed from the bottom of the bore hole.

FIGURE 3 is a sectional view taken along line 33 of FIGURE 1.

Referring now to the drawings in detail, the three cone bit in the embodiment of the invention depicted in the drawings includes a bit head designated generally by reference character which comprises a peripherally threaded shank portion 12 and a plurality of downwardly projecting, horizontally spaced legs 14. The legs 14 each rotatably journal a roller cone 16 with the three roller cones in the illustrated embodiment being severally designated 16a, 16b and 160. The roller cones 16a, 16b and 160 are each generally conically shaped in configuration, and are mounted on the legs 14 of the bit head 10 for rotation about their respective axes of symmetry. The axes of rotation and symmetry of the cones, when projected downwardly, converge in a common point which is disposed in the vertically extending axis of rotation of the drill string to which the bit head It) is attached. Stated differently, the axes of rotation of the several roller cones 16a, 16b and 160 pass through a common point located in the vertical axis of the bit head 10.

The roller cones 16a, 16b and 160 can be disposed symmetrically about the vertical axis of the bit head 10 or may be disposed asymmetrically thereabout. In the illustrated embodiment, the cones are symmetrically located with respect to each other and the vertical axis of the bit head 10, and have their vertical axes inclined with respect to a horizontal plane extending normal to the vertical axis of the bit head 10 at an angle of about 60.

Each of the roller cones 16a, 16b and 160 carry circumferential cutting teeth 18 which project radially outwardly from the roller cones and are provided with cutting edges, all of which lie in a common, imaginary conical surface forming an envelope extending coaxially around the conical body of the roller cone. Stated differently, the cutting edges of each of the cutter teeth 18 pass through a common imaginary line designated by reference character L in FIGURE 1 during the rotation of the roller cone about its rotational axis. At the base of each of the roller cones 16a, 16b and 160, a gauge tooth 20 is provided and is formed with a vertically extending side portion 22. The side portions 22 of the several gauge teeth 20 define the diameter of the bore hole which is drilled by the bit. If it is desired to obtain a greater overlap or interfit of the cutter teeth 18 of the adjacent roller cones, the gauge tooth on one of the roller cones may be omitted to permit the cones to be moved closer to each other without mutual interference between the several gauge teeth.

At the lower ends or apices of the several roller cones 16a, 16b and 160, a plurality of cylindrical extensions are provided. These vary in their length with the cylindrical extension on the roller cone 1611 being the longest, and designated by reference character 24, the cylindrical extension on roller cone 16c being slightly shorter than the cylindrical extension 24, and designated by reference character 26, and the cylindrical extension on the roller cone 16a being the shortest of the three cylindrical extensions and designated by reference character 28. Each of the cylindrical extensions 24, 26 and 28 are pressed into a cylindrical aperture or recess formed in the tip or apex of the respective cone'on which the cylindrical extension is mounted. The recesses for the cylindrical extensions 24 and 28 are illustrated in dashed lines in FIGURE 1 and are designated by reference characters and 32, respectively. The fit of the cylindrical extensions in their respective recesses is such that the extensions remain firmly in place though subjected to substantial vibration, and to forces tending to loosen them in their recesses during the drilling operation. Each of the cylindrical extensions 24, 26 and 28 is constructed of a hard material which is substantially more resistant to abrasion and wear than the metal of which the several roller cone cutter teeth is constructed. A preferred material of construction of the cylindrical extensions 24, 26 and 28 is tungsten carbide which has a hardness permitting it to outlast the cutting edges provided on the cutter teeth 18 and the gauge teeth 20 of the roller cones.

The distance which each of the cylindrical extensions 24, 26 and 28 extends downwardly from the respective roller cones 16a, 16b and upon which they are mounted is such that the cutting edge formed by the intersection of the flat end face of each of the cylindrical extensions and the cylindrical side wall thereof, lies in the same imaginary generally conical envelope that receives and contains the cutting edges of the several cutter teeth 18 and the gauge teeth 20. Described in another manner, the cutting edge formed on the cylindrical extensions by the intersection of the cylindrical side thereof with the end face thereof lies in the line L which has been described as being common to or receiving the cutting edges of the several cutter teeth 18 and the gauge teeth 20.

In the operation of the invention as described in the foregoing discussion, the hard metal cylindrical extensions 24, 26 and 28 bear against the central lowermost portion of the bore hole continually, and thus mill and fracture the small upwardly projecting cone or burr of earth which tends to develop in the center of the bore hole. The hole is thus continuously projected to the deepest extent at its exact center and the vertical alignment or straightness of the hole is better maintained for this reason. In other words, the lead drilling is accomplished toward the center of the hole. Moreover, the constant milling and fracturing action of the cylindrical extensions 24, 26 and 28 provides a free surface inwardly from the cutter teeth 18, and permits these teeth to chip and cut away the formation more efficiently than could be accomplished by the teeth if a cone or burr were permitted to extend upwardly from the center of the bore hole. Despite the fact that the cylindrical extensions 24, 26 and 28 are subjected to a greater amount of wear and abrasion, and have a greater stress placed on them than the several cutter teeth, the hardened metal permits the extensions to normally have a service life at least equal to that of the cutter teeth and usually substantially longer. In the event the cylindrical extensions 24, 26 and 28 do become worn or fractured, they can be removed from the cones 16a, 16b and 16c and replaced by new extensions without the requirement of replacing the entire roller cone.

From the foregoing description of the invention, it will have become apparent that the invention provides an improved roller cone type rock bit which efiiciently extends the bore hole vertically into the ground at a maximum rate. Moreover, the provision of the hardened metal cylindrical extensions at the vertices of the several roller cones permits the central and lowest portion of the bore hole to be continually kept clean and free of small burrs or cones extending upwardly therein which inhibit or retard the downward drilling action of the bit. Also, each of the cutter teeth and the gauge teeth are permitted to drill more efficiently by reason of the continual maintennance of a free surface at the center of the bore hole.

Although a preferred embodiment of the invention has been illustrated in the drawing and described in the foregoing description in order to provide an example sufficient to permit those skilled in the art to practice the invention, it will be understood that many modifications and variations can be made in the depicted and described structure without departing from the basic principles which underlie the invention. Insofar as changes of this type do not depart from the fundamental principles which permit the desirable results attributable to the invention to be achieved, they are deemed to 'be circumscribed by the spirit and scope of the invention except as the same may be necessarily limited by the appended claims or reasonable equivalents thereof.

What is claimed is:

'1. In a roller cone drill bit of the type having a plurality of conical roller cones rotatably mounted on the lower end of the drill string and each inclined downwardly and inwardly from its base to its apex, the improvement which comprises:

a cylindrical extension projecting downwardly and inwardly from the apex of one of the roller cones in coaxial alignment with the axis of rotation of said one roller cone whereby the cylindrical side wall and end face of said cylindrical extension define a cutting edge adapted to mill and cut the earth adjacent the center of a hole drilled by the bit.

2. A roller cone drill bit comprising:

a bit head having a geometric axis passing through the center thereof and having a plurality of horizontally spaced legs projecting therefrom in the same direction;

a roller cone rotatably mounted on each of said legs for rotation about the axis of symmetry of the cone, said roller cones having their apices spaced from said bit head and having their projected axes of rotation and symmetry converging in a point in the projected geometric axis of said bit head on the opposite sides of said roller cones from said bit head;

a plurality of cutter teeth projecting radially outwardly from each of said roller cones and each having a cutting edge extending normal to a line extending radially outwardly from the geometric axis of said bit head, the cutting edges of the teeth on each of said roller cones lying in an imaginary conical surface coaxially surrounding, and spaced outwardly from, the respective roller cone carrying the cutter teeth; and

a cylindrical extension carried by one of said roller cones and projecting from the apex thereof along the axis of rotation and symmetry of said one roller cone, said cylindrical extension having a cutting edge defined by the intersection of an end face and its cylindrical peripheral surface, said cutting edge lying in the same imaginary conical surface as that occupied by the cutting edges of the cutter teeth on the roller cone carrying said cylindrical extension.

3. A roller cone drill bit as claimed in claim 2. wherein said cutter teeth each extend circumferentially around the respective roller cone upon which they are mounted, and the several cutter teeth on each cone are spaced axially therealong in positions to interfit with, and project between, the cutter teeth on at least one adjacent roller cone.

4. A roller cone drill bit as claimed in claim 2 wherein said one roller cone is provided with a cylindrical recess at its apex and a portion of said cylindrical extension is pressed into said cylindrical recess.

5. A roller cone drill bit as claimed in claim 4 wherein said cylindrical extension is constructed of tungsten carbide.

6. A roller cone drill bit having a vertically extending axis of rotation and comprising:

a bit head formed symmetrically about said vertically extending axis of rotation and including an upwardly extending, peripherally threaded shank portion and a plurality of horizontally spaced, downwardly extending legs;

a roller cone rotatably mounted on each of said legs for rotation about its axis of symmetry, with the axes of symmetry and rotation of the several roller cones extending downwardly and inwardly through the apices of the cones and through a common point of intersection with the vertically extending axis of rotation of the drill bit;

cutter teeth projecting radially outwardly from each of the roller cones and terminating in cutting edges which lie generally in planes extending substantially normal to the axis of rotation of the respective roller cone on which the cutter teeth carrying the cutter edges are mounted and aligned along a common line; and

a cylindrical extension coaxially secured to at least one of said roller cones at the apex thereof and projecting from the apex of said one cone toward said common point of intersection, said extension being of a length such that the circumference of the circular end face of said cylindrical extension intersects the common line along which the cutting edges of said cutter teeth are aligned.

7. A roller cone drill bit as claimed in claim 5 wherein each of said roller cones is provided with one of said cylindrical extensions.

8. A roller cone rock bit having a vertically extending axis of rotation and comprising:

a bit head 10 formed symmetrically about said vertically extending axis of rotation and including an upwardly extending, peripherally threaded shank portion 12, and three horizontally spaced, downwardly extending legs 14, said legs being equally spaced from each other and from said vertically extending axis;

roller cones 16a, 16b and 16c rotatably mounted on each of said legs 14 for rotation about the axis of symmetry of the respective roller cone and with the axes of symmetry and rotation of the several roller cones 16a, 16b and 16c converging to a common point located in said vertical axis and below all of said roller cones 16a, 16b and 160, said roller cones 16a,.16b and 16c each being inclined with its apex disposed downwardly and inwardly toward said vertical axis from its base, each of said roller cones having a cylindrical recess formed coaxially therein and extending into each of the cones from the apex thereof;

a plurality of circumferentially extending, axially spaced cutter teeth 18 projecting from the conical, external peripheral surface of each of said roller cones 16a, 16b and 160, the cutter teeth 18 on each of said roller cones 16a, 16b and extending between, and interfitting with, the cutter teeth on another of said roller cones, said cutter teeth .18 each having a cutting edge extending in a plane perpendicular to the axis of rotation of the roller cone on which the respective cutter teeth 18 are mounted, and all of the cutter teeth 18 on each roller cone having their cutting edges lying in an imaginary conical surface coaxially surrounding the respective roller cone; and

a solid cylinder 24, 26 and 28 of tungsten carbide pressed into the cylindrical recess in each of said roller cones 16a, 16b and 160 and projecting downwardly and inwardly from the apex of the cone toward said vertical axis, the three solid cylinders being of diflferent lengths and diameters so as to avoid interference with each other as said roller cones 16a, 16b and 160 roll on the hole bottom about said vertical axis, said cylinders 24, 26 and 28 each providing a cutting edge defined by the intersection of the cylindrical side wall thereof with an end face thereof, the cutting edge of each solid cylinder 24, 26 and 28 lying in the imaginary conical surface which contains the cutting edges of the cutter teeth 18 carried on the same roller cone which carries the respective solid cylinder.

9. A roller cone drill bit comprising:

a bit head having a geometric axis passing through the center thereof and having a plurality of horizontally spaced legs projecting therefrom in the same direction;

a roller cone rotatably mounted on each of said legs for rotation about the axis of symmetry of the cone, said roller cones having their apices spaced from said bit head and having their projected axes of rotation and symmetry converging in a point in the projected geometric axis of said bit head on the opposite sides of said roller cones from said bit head;

a plurality of cutter teeth projecting radially outwardly from each of said roller cones and each having a cutting edge extending normal to a line extending radially outwardly from the geometric axis of said bit head, the cutting edges of the teeth on each of said roller cones lying in an imaginary conical surface coaxially surrounding, and spaced outwardly from, the respective roller cone carrying the cutter teeth; and

a cylindrical extension carried by each of said roller cones and projecting from the apices thereof along the axis of rotation and symmetry of each of said roller cones, said cylindrical extensions projecting differing distances from their respective roller cones toward such point of convergence of the projected axes of rotation and symmetry of the cones, each of said cylindrical extensions having a cutting edge defined by the intersection of an end face and its cylindrical peripheral surface, said cutting edge lying in the same imaginary conical surface as that occupied by the cutting edges of the cutter teeth on the roller cone carrying said cylindrical extension.

References Cited UNITED STATES PATENTS JAMES A. LEPPIN K, Primary Examiner.

R. E. FAVREAU, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,412,817 November 26, 1968 Donald R. Reichmuth It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 18, claim reference numeral "5" should read 6 Signed and sealed this 17th day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Commissioner of Patents Attcsting Officer WILLIAM E. SCHUYLER, JR. 

